Operating mechanisms to control the raising and lowering of doors have been used for many years. Among the doors so controlled are fire doors including fire doors of the type comprising a plurality of horizontal slats pivotally connected to one another to enable the fire door to be reeled in when raised and unreeled when lowered. There are numerous prior art mechanisms known and used for raising and lowering such fire doors both in normal or non-emergency conditions and during a fire. In such operating mechanisms, electric motors are commonly included to raise the door. However when a fire occurs, these operating mechanisms disengage the motor from the fire door and allow the door to close either under the urging of an auxiliary spring activated by mechanical means or by the gravitational pull on the door resulting from the release of tension from a torsion spring counterbalancing mechanism. Previously known fire doors primarily rely on mechanical means such as pendulum or oscillating governors, friction discs operating in viscous fluid baths, mechanical ratchets, cams or arms to release the fire door and govern its descent to secure the opening. However, these devices are unreliable because they often jam or cease functioning while the door is descending. The torsion spring counterbalancing mechanisms are also unreliable, expensive and difficult to adjust to assure that the door will move downwardly at a safe rate to a secure closed position. Centrifugally operative break type governors have also been employed to control the downward velocity of a fire door. However, such governors have always acted in conjunction with a low speed shaft connected to the door, which low speed shaft is difficult to control by devices responsive to centrifugal force. These problems are compounded by the fact that repeated use of the auxiliary springs and the springs in the counterbalancing mechanism often result in deformation due to excessive heating, as during a fire, and to general mechanical fatigue. Therefore, the need exists for an improved fire door operating mechanism for regulating the raising and lowering of the door which effectively controls the fire door's movement without the need of springs or unreliable mechanical means.